The new SL-650QDM includes even more features to protect against false and missed alarms caused by mis-alignment and environmental issues. With 650ft. of outdoor detection range and 4-channel beam frequency selection, the QDM model is perfect for high security perimeter applications. New features include: Dual modulation - Enhances signal discrimination against potential interferences Quad beam - Dramatically cuts down on false alarms caused by birds and falling leaves Sniper ViewFinder and Alignment Sound Assist - The new telescope lens on the SL Series has a high level of visibility for optical alignment work. Even at 650ft., a perfect installation and stable performance can be achieved in minimal time. Sunshine Protection Technology - The SL Series has triple layer construction to allow for better performance against external light sources. (The sun, car headlights, mercury-vapor lamps and fluorescent lights) Beam Power Control Selector - Allows you to manually adjust the beam power to help prevent crosstalk due to reflection, interference due to unstable signal or noise when using multiple beams over long distances, and allows the detector to be used in shorter than rated distances. Automatic Transmit Power Control - The A.T.P.C. automatically controls, adjusts and optimizes the power of the beam and maintains optimal performance. This decreases false and missed alarms caused by fog, frost, cross talk and signal saturation. BAU-4 Compatible - The BAU-4 beam alignment unit automatically and accurately adjusts the optical access. This allows peak performance and gives one technician the ability to align a 350ft or 650ft SL detector without additional help.